In a recent systematic review published in the journal Advances in Nutrition, researchers investigated the associations between nut consumption and fertility outcomes in human adults. Literature from four online scientific databases was collated and subjected to a meta-analysis. Following the full-text screening, four publications comprising 875 participants were included. Study findings revealed that consuming ≥ 60g nuts/day had profound beneficial effects on male fertility via increased sperm vitality and motility and improved sperm morphology compared to controls. While studies on the impacts of nuts on female fertility remain scarce, this study emphasizes that as little as two servings of nuts per day can significantly improve sperm parameters directly associated with fertility in men.
Review: Nut consumption and fertility: a systematic review and meta-analysis. Image Credit: Marie Sonmez Photography / Shutterstock
The growing issue of infertility
Infertility is a severe condition characterized by the inability to conceive despite 12 months of unprotected and regular sexual intercourse. Infertility has been observed to negatively affect couples’ social, financial, and psychological health, and its prevalence has been linked to parental age, nutrition, clinical health, and genetic hormonal disorders.
Infertility is a global concern, estimated to affect between 8-12% of all reproductive-age adults (18-49 years). Alarmingly, incidences of infertility are on the rise, especially in underdeveloped and developing countries, where one in every four couples experience difficulties in conceiving. In some areas, infertility rates are reported to meet or exceed 30%.
Despite substantial research into the causes and mechanisms of the condition, between 10-15% of infertility have no diagnosable underpinning. The primary intervention in these cases is the use of assisted reproductive technologies (ART). However, these interventions present a substantial financial burden, with a standard in vitro fertilization (IFV) cycle costing upwards of US$19,200.
“Considerable economic, racial, ethnic, geographic and cultural disparities in access to fertility treatments also exist, thus research aiming at maximising natural fertility is of utmost importance.”
Recent research has focused on identifying modifiable factors, including diet and health behaviors, that can improve fertility outcomes. The Mediterranean diet (MedDiet), characterized by high fish, fruit, and vegetable intake, remains the best studied, with findings suggesting that MedDiet adherence increases the number of available embryos and improves fertilization rate in previously subfertile women. In men, the diet has been associated with enhanced sperm concentrations and motility and increased sperm count.
Building upon the MedDiet, Gaksins et al. developed the Pro-Fertility diet, characterized by high concentrations of vitamins B12 and D and folic acid, aimed at maximizing female fertility and optimal fetal development. Given that pesticide use has been associated with lowered fertility and adverse fetal outcomes, the Pro-Fertility diet further prescribes low exposure to foods derived from pesticide-supplemented crops.
“While the studies that aim to establish a relationship between dietary patterns and fertility outcomes can provide insightful information, they may also represent a challenge to those who have very distinct dietary habits. Thus, identifying the benefits of particular foods can elucidate dietary strategies that are easier to be implemented.”
Nuts present an ideal potential solution for individuals adhering to the Western diet and similar suboptimal nutritional intakes. Nuts depict high concentrations of proteins, fibers, minerals, vitamins, and bioactive compounds with assumed benefits in fertility. Their ratios of Omega-3:Omega-6 fatty acids and low saturated fat concentrations have been found to suppress numerous chronic diseases related to cardiovascular and mental health.
About the study
The present study aims to investigate the associations between nut intake and positive fertility outcomes. It comprises a systematic review and meta-analysis and adheres to the referred Reporting Items for Systematic Reviews and Meta-Analyses (The PRISMA Statement) guidelines.
Data collection comprised searching four online databases, MEDLINE, Scopus, Embase, and CINAHL, from the inception till 30 June 2023 for all literature on diet (specifically nut consumption) and fertility. Inclusion criteria comprised any cross-sectional, cohort, case-control, or randomized clinical trial (RCT) that included human subjects of reproductive age (18-49) for a minimum duration of three months. The three-month period was enforced because regular sperm maturation cycles take 76 days to complete.
The Covidence Systematic Review Software was used for initial screening (title and abstract) and subsequent data extraction. The Cochrane Risk of Bias 2 and the Risk Of Bias In Non-randomized Studies–of Interventions (ROBINS-I) tools were used to assess included publications for methodology and outcome bias.
Statistical analyses comprised a random mixed effects model meta-analyses that evaluated the standardized mean difference (SDM) between case and control outcomes for each included study. The Cochrane Q statistic and I2 metrics were used to measure inter-study heterogeneity.
An initial database search identified 11,691 publications for title and abstract screening, of which 57 papers were retained. Full-text screening further discarded 53 papers, resulting in a final review dataset of 4 publications comprising 646 men and 229 women participants. All studies were included in the systematic review. Two studies were found to have high quality and low heterogeneity and were thus included in the meta-analysis.
Both included meta-analysis studies followed RCT methodologies and focused on the outcomes of nut consumption in men in tandem with a Western-style diet. Interventions included 60 – 75g of nuts or nut supplements provided daily for 12 weeks. Analyses revealed that cases (nut-supplemented males) were found to show significantly improved sperm parameters (motility, vitality, and morphology) compared to their control counterparts (no nuts in diet) following just 60g/day of nut consumption.
“In contrast, two non-randomised studies involving participants with varied fertility status found no convincing evidence for the association between dietary nut consumption of ≤ 1 serve per day and markers of sperm quality (men) or rates of embryo implantation, clinical pregnancy or live birth following ART (women and men).”
Interestingly, the Western-style diet is considered unhealthy and has been associated with severe mental and physical health conditions, including depression, cardiovascular disease, and cancers. Previous literature has correlated high Western diet adherence to declining male reproductive success. The finding that nut intake can not only reverse the demerits of the Western diet but also improve sperm parameters above the mean of the MedDiet highlights the importance of nut diet supplementation as a safe, natural, and inexpensive intervention against infertility.
Unfortunately, evidence for the beneficial impacts of nuts on female fertility is limited. Future research should investigate this association, and if findings are positive, recommend nuts to healthcare practitioners and prospective parents as a key behavioral modification in improved fertility outcomes.